Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
  • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C47/00—Making alloys containing metallic or non-metallic fibres or filaments
  • C22C47/02—Pretreatment of the fibres or filaments
  • C22C47/06—Pretreatment of the fibres or filaments by forming the fibres or filaments into a preformed structure, e.g. using a temporary binder to form a mat-like element
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C47/00—Making alloys containing metallic or non-metallic fibres or filaments
  • C22C47/08—Making alloys containing metallic or non-metallic fibres or filaments by contacting the fibres or filaments with molten metal, e.g. by infiltrating the fibres or filaments placed in a mould
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C49/00—Alloys containing metallic or non-metallic fibres or filaments
  • C22C49/02—Alloys containing metallic or non-metallic fibres or filaments characterised by the matrix material
  • C22C49/08—Iron group metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• This invention relates to the production of metal matrix composites, and more particularly to preforms of reinforcing material used in such composites.
• MMC metal matrix composites
• One of the most popular techniques used to manufacture metal matrix composites is melt infiltration. In this procedure a preform of preferably fibrous reinforcing material is infiltrated under pressure by liquid metal. The preform must maintain its physical integrity, i.e., it must not fracture throughout the infiltration procedure. In order to accomplish this, chopped fibres of the reinforcing material are coated with a binder, such as a SiO2 based suspension, filtered into a cake and then calcined to drive off the moisture and form a rigid preform.
• a binder such as a SiO2 based suspension
• the rigid preform thus formed contains solid SiO2 and infiltrating liquid aluminum reacts with the SiO2, reducing it to free silicon.
• the result is the formation of large silicon particles adjacent the fibres. These silicon particles have poor physical properties and generally degrade the ultimate performance of the composite. For many uses of the metal matrix composites, this loss of properties can be tolerated. However, the loss cannot be tolerated when the metal matrix composites are used in high temperature applications where thermal fatigue is an important consideration.
• a satisfactory preform can be produced by bonding reinforcing fibres together using colloidal alumina as the bonding agent in place of SiO2.
• colloidal alumina as the bonding agent in place of SiO2.
• the absence of SiO2 in the preform means that a composite is formed which is free of silicon associated with the decomposition of SiO2.
• the infiltrating melt is a silicon-­containing alloy, a composite is obtained in which there is no preferential nucleation of the silicon phase at the fibres of the preform.
• one embodiment of this invention comprises a novel preform in which randomly oriented reinforcing fibres are bonded together using colloidal alumina as the bonding agent.
• the reinforcing fibres are preferably ⁇ -alumina fibres, such as Saffil® fibre. While any colloidal alumina may be used, a preferred colloidal alumina is a product of chi-alumina rehydration, which is formed during attritor grinding. This colloidal alumina has a pH of 2-4 with pseudo-boehmite-like structure and, after calcination at 500-550°C, shows a gamma-alumina structure.
• the preform may be prepared by mixing the colloidal alumina in an aqueous solution with chopped alumina fibre and filtering the slurry into a cake. The cake is then calcined to drive off the moisture and produce a rigid preform.
• the bulk density of the preform can be controllably varied within wide limits, typically over a range from about 5% to about 50% of the density of the component fibres, by appropriate selection of compacting pressure.
• the compacting pressure may be exerted by vacuum drawing the slurry of fibres against a perforate wall or screen, and/or by a press.
• a further embodiment of the invention is a process for forming a composite cast article comprising an aluminum-­silicon alloy matrix containing a modifier to reduce the particle sizes reached by the silicon during eutectic solidification and a preform of bonded together Al2O3 fibres incorporated in the matrix.
• a composite cast article having superior physical properties is obtained when the preform is infiltrated under pressure by a melt of the modified aluminum-silicon alloy and the composite article thus formed is allowed to solidify by cooling.
• Excellent composite articles are obtained when the usual additives for Al-Si alloys, e.g. alkali metals or alkaline earth metals, such as sodium or strontium, are used in the usual amounts.
• Typical aluminum silicon alloys for this purpose contain about 5 to 15 percent by weight silicon and such alloys are typically modified by addition of about 0.03 to 0.07 percent by weight strontium or about 0.0005 to 0.001 percent by weight sodium.
• the procedure of the present invention is particularly effective when used in the method of producing composite cast articles described in EP-A-0271222.
• a preform of reinforcing material was prepared from 3 ⁇ m diameter alumina fibre (Saffil ® fibre available from ICI). The fibre was chopped into lengths of about 200 ⁇ m and an aqueous slurry was formed containing 5% by weight coiloidal alumina and 100 g/l of the Saffil fibre.
• the colloidal alumina was a product of chi-alumina rehydration formed during attriter grinding, having a pH of 2-4 with pseudo-boehmite-like structure and, after calcination at 500-550°C, showing a gamma-­alumina structure.
• the slurry was mixed and poured into a suction filter to form a cake of coated fibre.
• the cake was then placed in an oven and heated at 500°C for 4 hours to drive off the moisture and produce a 30 volume % rigid preform having a height of 30 mm and a diameter of 70 mm.
• a further firing at 1000°C for 2 hours was used to remove remaining water of hydration.
• the above preform was heated to 800°C and placed into a 75 mm diameter die preheated to 500°C.
• a melt of super purity aluminum (Alcan 99.87%) was immediately poured on top of the hot preform and a cold ram (25°C) was used to force the molten aluminum into the porous preform.
• the infiltration pressure was nominally 20 MPa and sufficient of the melt was used to totally infiltrate the preform and result in a composite with free matrix aluminum both above and below the preform.
• the composite thus formed was allowed to solidify by cooling to obtain the desired composite cast article.
• a cross section of the composite cast article was subjected to metallographic examination by means of optical microscopy, scanning electron microscopy and differential scanning calorimetry and there was no evidence of silicon formation.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)

Applications Claiming Priority (2)

Publications (1)

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Cited By (5)

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Citations (3)

• 1988
  • 1988-10-13 EP EP88309592A patent/EP0313271A1/en not_active Withdrawn
  • 1988-10-19 KR KR1019880013723A patent/KR890006842A/ko not_active Application Discontinuation
  • 1988-10-19 BR BR8805398A patent/BR8805398A/pt unknown
  • 1988-10-20 JP JP63266998A patent/JPH01147031A/ja active Pending

Patent Citations (3)

Non-Patent Citations (1)

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